Oil sands ore is a mixture of bitumen, minerals including clays and sands, and water. Recovering bitumen from the ore begins with excavating the ore, such as by using a shovel in an open pit mine. Trucks deliver the excavated ore in discrete deliveries to a hopper, which in turn feeds the ore to a crusher. The crushed ore is mixed with water and steam to form a slurry. A pipeline hydro-transports the slurry to an extraction facility where it is subjected to gravity separation in a primary separation vessel (PSV) to produce a bitumen froth process stream and a tailings stream. The bitumen froth is further treated with light hydrocarbon solvent and subjected to mechanical separation processes to recover bitumen.
The quality of ore used to make the slurry affects bitumen recovery at the extraction facility. For example, in comparison to ores having high grade (i.e., bitumen content of about 10 to 12 percent or higher) and low fines content (i.e., less than about 20 percent), ores that have low grade (i.e., bitumen content of about 6 to 10 percent) and high fines content (greater than about 30 percent) tend to be associated with lower bitumen recovery to the froth, and greater bitumen loss to the tailings. The challenge of maintaining a desired bitumen recovery rate at the extraction facility is compounded by variations in ore quality throughout the ore body, and potentially, limited amounts of high grade, low fines ore.
In order to produce an oil sands ore feedstock of relatively constant composition for the extraction facility, ores of different qualities may be roughly blended when producing the slurry. Current ore blending practices attempt to control only two ore characteristics in the ore blend: ore grade (bitumen content) and fines content (i.e. the content of solid particles having a diameter less than 44 microns). These characteristics are used to control bitumen extraction process parameters such as caustic dosage, and water addition. Feed rate of the slurry may also be varied based on production requirements, and in response to excursions in bitumen recovery observed at the extraction facility.
However, current ore blending practices are not always satisfactory. Despite controlling ore grade and fines content within acceptable ranges, actual bitumen recovery may vary significantly from expected recovery. This may be due to the effect of numerous other ore characteristics, and their interaction with each other, that are important or even critical to bitumen recovery. Moreover, current ore blending practices are not based on predicted bitumen recovery, and make it difficult to identify causes of poor ore processability and appropriate coping strategies.
The planned delivery sequence of ores to the hopper can also be upset by equipment breakdown and downtime, and limited capacity of the surge piles at the hopper. These upsets may be undiagnosed until several hours later when an increase in bitumen loss to the tailings is noticed at the extraction facility. By then, however, it is too late to take remedial action in respect to either ore blending at the hopper, or process control at the extraction facility that would positively impact the material already being processed at the extraction facility.
Accordingly, there is a need in the art for improvements to ore blending practices with a view to controlling bitumen recovery from ore bodies in bitumen extraction processes.